Some processes which are commonly employed in the production of bisphenol and are based on the reaction of phenol with 3,3,5-trimethylcyclohexanone conducted in the presence of an acid and a thiol are known in the art as being available for the production of 3,3,5-trimethylcyclohexylidenebisphenols, especially 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane being a reaction product of phenol and 3,3,5-trimethylcyclohexanone.
For example, Japanese Patent Laid-open Publication No. 2(1990)-88634 discloses a process for producing 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, which comprises reacting phenol with 3,3,5-trimethylcyclohexanone at a molar ratio (phenol/3,3,5-trimethylcyclohexanone) of 6/1 in the presence of a catalyst consisting of hydrogen chloride gas and an alkylmercaptan and removing unreacted phenol from the resultant reaction mixture by steam distillation.
Further, Published Japanese Translation of PCT Patent Applications from Other States, No. 8(1996)-505644 discloses a process for producing 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, which comprises reacting phenol with 3,3,5-trimethylcyclohexanone in the presence of a reaction promoting catalyst consisting of a mixture of hydrochloric acid and an alkanethiol such as octanethiol to thereby obtain a reaction mixture containing 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane as an adduct of phenol and 3,3,5-trimethylcyclohexanone and separating 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane from the reaction mixture.
Still further, Published Japanese Translation of PCT Patent Applications from Other States, No. 9(1997)-507250 discloses a process for producing 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, which comprises reacting a ketal or thioketal with phenol, the ketal or thioketal being to be synthesized from 3,3,5-trimethylcyclohexanone and a diol or mercaptoalcohol.
Moreover, Japanese Patent Laid-open Publication Nos. 5(1993)-213803 and 4(1992)-282334 disclose processes applicable to continuous processing, which comprise reacting a cyclohexanone with a phenol in the presence of an anhydrous insoluble cation exchange resin containing sulfonic groups (acidic anhydrous condensation catalyst) and .beta.-mercaptopropionic acid or the like as a co-catalyst to thereby obtain a substituted cyclohexylidenebisphenol.
However, when 3,3,5-trimethylcyclohexanone is used as a starting material, the reaction is extremely slow (conversion of ketone 24 hr after the initiation of the reaction: 55%, see Comparative Example c) of Japanese Patent Laid-open Publication No. 4(1992)-282334). Further, the selectivity of 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane is low (selectivity: 72%, see Example 6 of Japanese Patent Laid-open Publication No. 5(1993)-213803).
A continuous reaction processing provides effective means for enhancing the efficiency in commercial production. Continuous feeding of a reaction mixture can be mentioned as one of the requirements for the continuous reaction processing.
However, 3,3,5-trimethylcyclohexylidenebisphenols, especially 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, have the property of causing the viscosity of the reaction mixture to be abnormally high when the reaction is proceeded. Therefore, when the conventional processes described in the above publications are employed, either it is difficult to continuously feed a reaction mixture under conditions enhancing a reaction yield or, although a reaction mixture can be continuously fed, not only is the reaction rate extremely low but also the selectivity is poor.
Therefore, there is a demand for the development of a process for producing a 3,3,5-trimethylcyclohexylidenebisphenol, which process enables not only suppressing a rise of the viscosity of the reaction mixture but also obtaining the desired 3,3,5-trimethylcyclohexylidenebisphenol at high yield, and which process is applicable to not only the productivity enhancement in batch operation but also a continuous reaction processing.